Respiration (Edexcel International A Level (IAL) Biology): Flashcards

During glycolysis, glucose is phosphorylated (using 2 ATP) to hexose bisphosphate, which is then split into two molecules of triose phosphate.

The net gain of ATP molecules during glycolysis is 2 per glucose molecule.

Glycolysis produces 2 pyruvate molecules, a net gain of 2 ATP and 2 reduced NAD (NADH) per glucose molecule.

Phosphorylation in glycolysis is the addition of phosphate groups to glucose using ATP, making glucose more reactive and allowing glycolysis to proceed.

Triose phosphate is oxidised (it loses hydrogen) to form pyruvate. The hydrogen is collected by NAD, forming reduced NAD (NADH).

Under anaerobic conditions, glycolysis produces lactate (lactic acid) instead of pyruvate.

The link reaction is the stage in aerobic respiration where pyruvate is oxidised and decarboxylated in the mitochondrial matrix to form acetyl CoA, carbon dioxide and reduced NAD, linking glycolysis to the Krebs cycle.

The end product of glycolysis is pyruvate. When oxygen is available, pyruvate enters the mitochondrial matrix by active transport and takes part in the link reaction.

Pyruvate enters the mitochondrial matrix from the cytosol by active transport.

True.

No ATP is produced during the link reaction.

The Krebs cycle is a series of enzyme-controlled reactions in the mitochondrial matrix that oxidises acetyl CoA to produce reduced NAD, reduced FAD, ATP and releases CO₂.

During the Krebs cycle, the 2C acetyl group from acetyl CoA combines with oxaloacetate to form citrate.

The Krebs cycle is cyclical because the acceptor molecule oxaloacetate is regenerated at the end of the cycle so it can combine with another acetyl CoA and continue the process.

Each molecule of glucose results in two turns of the Krebs cycle.

Oxidative phosphorylation is the final stage of aerobic respiration, occurring at the inner mitochondrial membrane, where energy from electrons is used to produce ATP and water.

Oxidative phosphorylation occurs at the inner mitochondrial membrane.

During oxidative phosphorylation, oxygen acts as the final electron acceptor, forming water at the end of the electron transport chain.

The chemiosmotic theory explains how energy from electrons is used to pump protons across a membrane, creating a gradient that drives ATP synthesis through ATP synthase.

The main products of the electron transport chain are ATP and water.

Protons flow back into the mitochondrial matrix through ATP synthase, which then uses this energy to phosphorylate ADP to ATP.

The electron transport chain is a series of membrane proteins that pass electrons and use their energy to pump protons across the inner mitochondrial membrane.

False.

For every reduced NAD molecule, 3 ATP molecules are produced during oxidative phosphorylation.

Hydrogen atoms from reduced NAD and FAD are split into protons and electrons.

Oxygen is essential because it acts as the final electron acceptor, allowing the electron transport chain to continue and enabling the regeneration of NAD and FAD.

For every molecule of glucose, aerobic respiration produces up to 38 molecules of ATP.

Anaerobic respiration is the production of ATP in cells under conditions of little or no oxygen.

When there is no final acceptor of electrons from the electron transport chain, the chain stops functioning.

No more ATP is produced via oxidative phosphorylation when oxygen is not available.

Without oxygen, reduced NAD and FAD are not oxidised by an electron carrier.

False.

The Krebs cycle stops when there is no oxygen.

Cells can continue glycolysis in low oxygen by oxidising the reduced NAD produced during glycolysis, allowing a small amount of ATP to be produced.

Lactate fermentation is an anaerobic pathway in which reduced NAD transfers hydrogen to pyruvate, forming lactate and allowing NAD to be reused in glycolysis.

In lactate fermentation, pyruvate is reduced to lactate by the enzyme lactate dehydrogenase.

Lactate can be oxidised back to pyruvate for the Krebs cycle or converted into glucose by the liver for storage or respiration.

Ethanol fermentation is an anaerobic pathway where pyruvate is decarboxylated to ethanal, then ethanal is reduced to ethanol. It occurs in yeast and plant cells.

The respiratory quotient (RQ) is the ratio of carbon dioxide produced to oxygen consumed during respiration.

The formula for calculating the respiratory quotient (RQ) is: RQ = CO₂ ÷ O₂.

The typical RQ value for aerobic respiration of glucose is 1, meaning equal amounts of carbon dioxide are produced to oxygen consumed.

True.

An RQ value greater than 1 indicates that more carbon dioxide is produced than oxygen consumed, which is typical of anaerobic respiration.

Carbohydrates, lipids, and proteins have different RQ values because the number of carbon-hydrogen bonds differs in each molecule.

You can compare the measured RQ value to the typical RQ values for carbohydrates, lipids, and proteins to suggest which substrate is being respired.

The approximate RQ value for a lipid is 0.7, because lipids contain many carbon-hydrogen bonds and require a large amount of oxygen to be respired.

The typical RQ value for a protein being respired is approximately 0.9.

A redox indicator is a substance that changes colour when it is reduced or oxidised.

DCPIP and methylene blue are used as redox indicators to monitor the rate of respiration in yeast by changing colour when reduced.

The colour change from blue to colourless indicates the reduction of DCPIP or methylene blue.

The effect of substrate concentration on the rate of respiration in yeast is being investigated.

Dehydrogenase is an enzyme that catalyses the removal of hydrogens from substrate molecules, producing reduced NAD in glycolysis.

The rate of respiration is inversely proportional to the time taken for the colour change.

Keeping the volume of dye and yeast suspension constant ensures that the rate of colour change accurately reflects changes in respiration rate and is not affected by the amount of dye or yeast present.

True.

At extreme high temperatures, dehydrogenase can become denatured, so the dye does not change from blue to colourless.

A respirometer is an apparatus used to measure the rate of oxygen consumption during respiration in organisms.

A respirometer experiment often uses germinating seeds (organisms) and glass beads as a control.

Soda lime or potassium hydroxide is used to absorb the carbon dioxide produced during respiration in a respirometer.

The formula used to calculate the volume of oxygen consumed is πr²h.

A positive y value means the manometer fluid moved up towards the test tube containing the seeds.

The RQ can be calculated by measuring the volume of oxygen consumed and the volume of carbon dioxide produced using the respirometer, then applying the formula: RQ = CO₂ produced / O₂ consumed.

An RQ greater than 1 indicates anaerobic respiration (or carbohydrate being converted to lipid), while an RQ less than 0.7 indicates lipid or protein is being respired.

The respiratory quotient (RQ) is the ratio of the volume of carbon dioxide produced to the volume of oxygen consumed during respiration.

True.

An RQ value of 1 means that only carbohydrates are being respired.

You can repeat the experiment and use an average, and use a controlled water bath to keep the temperature constant.